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Van Shahan (1954-2010) was a American inventor, inventor, VLSI design engineer and author who was involved in the development of Motorola's MC68881, MC68882, MC68040 , MC68060, andPowerQuicc microprocessors and systems on a chip. During his 30+ years of service, he was granted many patents and has been described as "an absolute legend at Motorola/Freescale and in the chip design community”.

Education

Shahan held BSEE degree (1979) from the University of Texas in Austin.

Career

From 1979 to 2005, he was a Senior Design Engineer at Motorola, where he specified and designed the microcode and the controller core of the MC68881 floating point coprocessor for the MC68020, second generation of the Motorola 68000 series instruction set architecture microprocessors designed for the engineering workstation and Apple Macintosh personal computer.

68020 and 68881 Development (1980-1985)

The design goal for the MC68020 and the [[Motorola 68881|MC68881] was to deliver comparable computing performance against the DEC VAX-11/780. All these designs had the software focus of delivering high performance engineering computation in C-language programs running on the Unix OS. For this market, superior floating point arithmetic performance was a key market benchmark.

The compelling microprocessor-based systems in 1981 were the IBM PC, the H-P and Apollo engineering workstations and the Apple Lisa. In 1982, Motorola knew that Apple's Macintosh development was based on the 68000. Although the Macintosh would not hardware floating point for several years, it would provide a volume driver the 68K family of system chips.

68881 Floating Point Co-processor Development

The Intel 8087 and Motorola 68881 were the principle VLSI drivers for the IEEE 754 floating point arithmetic spec in the engineering workstation market. Floating point arithmetic was common in IBM mainframes and was an option in the DEC PDP-10 mini-computers. Motorola made the decision to co-develop the 68881 FPU with the 68020, the second generation of the 68000, the 68020. The target market was engineering workstations from HP and Apollo.

The 68020 was designed as a single-chip competitor to the VAX-11/780, the next generation DEC mini-computer. Microprocessor design in 1980 was led by Gary Daniels. Key members of his staff were Mike Wiles, System Design, Gene Schriber, Circuit Design and Wayne Bussfield, CAD/Layout. Each project had two teams with the Systems design (systems) member and the Circuit design (circuits) member each leading the respective teams in a two-in-a-box management. The 68020 was headed by David Mothersole, systems, and Bob Thompson, circuits. The 68881 was lead by Stan Groves, systems, and Ashok Someshwar, circuits. Van Shahan and Kirk Holden were lead implementers of systems and circuits respectively.

Van's primary role was managing the interpretation of the Floating Point Specification, IEEE 754. This was a critical role for the 881 since both systems and circuit design depended on a careful and thorough understanding of compliance to a strict specification of a conforming standard. The 68020 and the 8086 CPUs did not have such restrictions as Motorola and Intel owned the instruction set architecture and could make any reasonable modification to achieve performance and die size targets. The x87 and the 881 had to conform to the IEEE spec religiously while communicating with the processor over a co-processor bus.

The 020 and the x86 were both microcoded machines. The 881 and the x86 were microcoded as well. The implications of this style of design was that microcode, a form of firmware, required many clock cycles to compute both floating point multiple and divide algorithms. The nature of microcode was that because of size limitations in the microcode ROM, many microcode instructions needed to be shared among many different machine instructions. The 881 microcode was written by Paul Harvey and Clay Huntsman.

Van's attention to detail was phenomenal and this was the birth of Van's impressive bible of note-taking; the yellow legal pad and the special pen with a silver barrel and medium black ink. The legal pad and the pen became a signature of the most impressive set of notes for any meeting that Van attended. He could argue persuasively for a fine point of interpretation of the floating point spec while comprehensively recording all of the competing voices in the room. Everyone read the spec but only Van absorbed it into his pores.

68030 and 68882 development (1984-1985)

The 68030 had an integrated memory management unit while Shahan's '882 incorporates several design enhancements.

68040 development

The 68040 integrated the processor, the floating point unit and the memory unit on a single die. Van was the primary interface between the business unit and the design team. Apple had been a principle customer of the 68030 but the 040 was targeted at the engineering work station with HP/Apollo and EMC as driving customers. Shahan was the Main Architect, Systems Project Leader and driving force behind the 68040 project. He was also a critical part of Motorola’s success in the workstation market.

PowerPC Somerset design center

Apple made the design decision to halt 68K-based product development with the 68040 and switch to the IBM PowerPC architecture. The original sole-IBM PPC601 was the first PowerPC-based Apple product. The Somerset design center was a joint development effort of Apple, IBM and Motorola. The PPC603e was the low-power CPU developed for the Apple laptop/portable product. Motorola created the e300 hign -performance embedded processor from the 603e. Shahan joined the high-performance embedded development team in 1996.

==Embedded (non-Apple) PowerPC - MC6240 (Kahlua)and MC8260 (PowerQuicc II) development The MC6240, code-named Kahlua, integrated the Apple portable/laptop motherboard. This comprised the e300 Book E (embedded PPC spec)CPU and the PPC 106 northbridge. The system and circuit bill of materials for Kahlua MC8240 thereby included a general purpose CPU plus FPU, an SRAM memory controller and a PCI controller. The Motorola Semiconductor Israel Limited (MSIL) design team added the advance ethernet packet processor Quicc Engine to Kahlua to form the 8260 PowerQuicc II. These designs eventually appeared as enhanced versions labeled the MC834x and MC836x to reflect the e300 embedded processor designation.

MC8560 e500 based PowerQuiccIII

The e500 (elf) core was a design derivative of the PPC750, the second generation Apple portable/laptop processor. The 8560 included an advanced northbridge function that included PCI express and the advanced Quicc Engine with Gigabit Ethernet. 8340/60 8560 QorIQ